Global Exploration of the Conditions of Downward Terrestrial Gamma-ray Flash (TGF) Production

这个项目试图了解地球伽马射线闪电何时、何地和为什么伴随着闪电。TGFs是一种强烈的高能辐射爆发，是在雷暴发生时由绕地球轨道运行的卫星首次发现的。在能量释放区域几百米范围内的飞机上，它们会释放出足够的辐射，对人类健康构成威胁。也许最神秘的是，绝大多数闪电不会产生转化生长因子，我们还不知道有转化生长因子的闪电有什么特别之处。已经观测到的大多数TGFs都是向上指向太空的，但也有向下的TGFs，它们的观测次数要少得多，而且似乎与非常不同类型的闪电有关。辐射传感器将部署在世界各地闪电丰富但其他方面不同的环境中--高海拔和低海拔地区，以及夏季强闪电和冬季强闪电的地点。探测到和没有探测到的转化生长因子将与无线电波上的数据进行比较，以显示发生了何种闪电。这将有助于理清何时最有可能出现TGFs，并有助于深入了解它们是如何发生的。部署地点将包括Mt.圣蒂斯在瑞士和山上。富士在日本，最近被证明是夏季闪电产生TGFs，以及日本西海岸，在那里，多年来一直知道冬季雷暴在地面附近产生TGFs。这些环境中的TGFs是由正向和负向内闪电、自然负向云对地闪电以及从塔上向上的正向引导者引发的负向云对地闪电产生的。观测将使用新开发的探测器阵列进行，这些探测器具有精确的(微秒)计时和各种大小的探测器，以显著提高动态范围(以便可以很容易地表征微弱/遥远和明亮/附近的TGFs)。除了现有的探测器，还将部署一种新型探测器；这是一种亚秒级时间分辨率的数字剂量计，它将量化TGFs的辐射剂量，距离如此之近，以至于所有传统探测器都进入饱和或关闭。我们将研究TGFs和相关SFRIC的特征，以寻找与云对地闪电和云内闪电相关的TGFs之间的系统差异；与唯一强大SFRIC相关的TGFs和仅具有弱SFRIC的TGFs之间的系统差异；以及从另一个角度来看，产生TGFs的闪电和不产生TGFs的闪电的特征，所有这些都是为了澄清产生机制(例如，不同几何结构的相对论反馈与领导者产生种子电子的情况)。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This program seeks to understand when, where, and why terrestrial gamma-ray flashes (TGFs) accompany lightning. TGFs are intense bursts of high-energy radiation that were first discovered by satellites orbiting Earth when thunderstorms were taking place below. They emit enough radiation to pose a health risk to humans aboard an aircraft within a few hundred meters of the region of energy release. Perhaps most mysteriously of all, the vast majority of lightning flashes don't produce a TGF, and we don't yet understand what's special about the ones that do. Most of the TGFs that have been observed have been directed upward toward space, but there are also downward TGFs, which have had far fewer observations and appear to be associated with very different types of lightning. Radiation sensors will be deployed to environments around the world that are all rich in lightning but otherwise diverse -- high and low altitude sites, and sites with strong summer lightning and strong winter lightning. TGF detections and non-detections will be compared with data on radio waves that show what kind of lightning occurred. This will help sort out when TGFs are most likely to be expected, lending insight as well into how they happen.Deployment sites will include Mt. Santis in Switzerland and Mt. Fuji in Japan, where it has very recently been shown that summertime lightning produces TGFs, and the west coast of Japan, where it has been known for several years that winter thunderstorms produce TGFs close to the ground. TGFs in these environments have been produced by positive and negative intracloud lightning, by natural negative cloud-to-ground lightning, and by negative cloud-to-ground lightning initiated by an upward positive leader from a tower. Observations will be made with newly developed detector arrays that have accurate (microsecond) timing and detectors of a range of sizes to dramatically improve dynamic range (so that faint/distant and bright/nearby TGFs can be easily characterized). A new type of detector will be deployed alongside the existing ones; this is a digital dosimeter with sub-second time resolution that will quantify the radiation dose from TGFs so close that all the conventional detectors go into saturation or shut down. Characteristics of the TGFs and associated sferics will be searched for systematic differences between TGFs associated with cloud-to-ground and intra-cloud lightning; TGFs associated with uniquely powerful sferics and those with only weak sferics; and, from the other perspective, characteristics of lightning that produces TGFs versus lightning that doesn't, all with the goal of clarifying the production mechanisms (e.g. relativistic feedback in different geometries versus production of seed electrons by leaders).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.